There is considerable prior art relating to the use of hydroxycarboxylic acids, in particular alpha-hydroxycarboxylic acids such as glycolic acid and lactic acid, in skin care applications. Alpha-hydroxycarboxylic acids are basically used as chemical versions of facial scrubs. When applied topically, they accelerate the sloughing off of dead cells from the outer layer of the skin, the stratum corneum, forcing the underlying cells in the epidermis to accelerate the creation of fresh new cells to replace them. The body may also attempt to repair this minor damage, by depositing new collagen in the underlying dermal layer. The net apparent result is smoother, firmer, more evenly pigmented skin reminiscent of the person's skin at an earlier time chronologically. See generally, web page found at http://www.thriveonline.com/@@62AH9wYA2@Hgbb2a/thrive/health/skinsave.intr o.html (Jul. 9, 1997 11:29 AM).
There are known side effects associated with the use, and in particular the prolonged use, of alpha-hydroxycarboxylic acids. These include acute skin irritation on application of the alpha-hydroxycarboxylic acid with possible development over time of an allergic-like reaction to such applications with some patients, and increased sun sensitivity.
Various techniques have been employed to decrease the side effects of alpha-hydroxycarboxylic acids such as partial neutralization, which increases the pH of the applied product (see Market View, The U.S. Cosmetics Industry, "Special Report, AHA Consumer Products 1990-1993," p.6.); partial or complete esterification, which also increases the pH of the applied product (see Genetic Engineering News dated Apr. 1, 1996 found at http://www.dc.enews.com/magazines/geng.sub.-- news/archive/960401005.html on Jul. 9, 1997); or the use of additives (see, Hahn, "A New Line of Defense Against Aging: Breaking the Irritation Barrier," DCI, January 1998). See also, generally, Parab, U.S. Pat. No. 5,420,105; Habif et al., U.S. Pat. No. 5,690,947; Hahn et al., U.S. Pat. No. 5,716,625; De Lacharriere et al., U.S. Pat. No. 5,714,155. None of these approaches change the real interaction of the alpha-hydroxycarboxylic acid with the epidermis. Rather, they provide the appearance of irritation reduction.
None of the current "solutions" to the irritation problem of alpha-hydroxycarboxylic acids has approached the problem by changing the delivery mechanism of the active ingredient such that it does not irritate the outer layers of the skin, yet the active ingredient targets the lipid-rich layers of the skin, more efficiently delivering free alpha-hydroxy-carboxylic acid to those sites in the epidermis where the new cells are created.
Alpha-hydroxycarboxylic acid derivatives which have the ability to efficiently deliver free alpha-hydroxycarboxylic acids to preferred sites in the epidermis to promote new cell and collagen growth without irritation of the skin and with no associated toxicity concerns have clearly been sought for years to no avail. Associated with such a material would also be the desire for a simple high yield manufacturing process to make the material in the very high purity normally associated with cosmetic ingredients.